This invention relates to a variable low pass filter which is remotely controllable and more particularly to a chroma key soft edger.
In a chroma keying system, the red, green and blue video signals from a camera are received by a chroma keyer which in response to a particular color signal provides a relatively high amplitude keying signal which exceeds a given threshold level. When a special effects device receives this keying signal, the device causes an electronic switch to switch from one camera to a different camera for the duration of that keying signal. It has been found that if this keying signal switches the electronic switch too rapidly, the rapid change in video causes bearing and noise generating effects which are undesirable. Broadcasters and users of such equipment are requesting some form of more gradual switching from one camera to the other so as to prevent these beating and noise effects. Since this switch which is switching the cameras may be located at a point remote from the controller, it is also desirable to have the control signal processing means be remotely controlled in order for the operator in the studio control room to vary the switching time for special effects and for eliminating the beating noise effects. It is therefore desirable that the chroma control signal which is going to control the switcher have a variable rise time which is selectable from a remote location.